This paper presents a three-dimensional numerical analysis of multiple fracture growth leading to the development of excavation disturbed zones and spalling around deposition boreholes in a geological disposal facility. The development of fracture patterns is simulated with the Imperial College Geomechanics Toolkit, a finite-element based simulator that can model the simultaneous nucleation, growth, and coalescence of multiple fractures in quasi-brittle rock. In these simulations, fractures develop due to the stress concentrations around the borehole wall, caused by the local in situ stresses, and due to the thermal stresses caused by the radioactive decay of the waste. Fracture patterns, and the extent of the spalled zone, are computed after the borehole drilling, heating, and cooling stages, at the Forsmark repository site in Sweden. The effect of temperature on the nucleation and growth of spalling fractures, as well as on the reactivation of pre-existing fractures, is assessed qualitatively, by comparing fracture patterns, and quantitatively, in terms of the maximum spalling depth, width, and increase in the total fractured surface area. Overall, the simulations presented herein indicate that thermal spalling will increase the depths (away from the borehole) and angular widths of the spalled zone, but is not likely to lead to major increases in fracture aperture, and concomitant increases in hydraulic transmissivity and permeability of the spalled zone, above that which has already been caused by mechanical spalling.

中文翻译：

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地下核废料储存库热相期间沉积钻孔周围剥落的热力学模型


本文对多条裂缝的增长进行了三维数值分析，该分析导致了地质处置设施中沉积钻孔周围开挖扰动带和剥落的发展。Imperial College Geomechanics Toolkit 是一款基于有限元的模拟器，可以模拟准脆性岩石中多个裂缝的同时成核、生长和合并。在这些模拟中，由于局部原位应力引起的井壁周围的应力集中以及废物放射性衰变引起的热应力，会形成裂缝。在瑞典的 Forsmark 储存库站点进行钻孔、加热和冷却阶段后，计算出裂缝模式和剥落带的范围。通过比较裂缝模式，定性评估温度对剥落裂缝的成核和生长以及先前存在的裂缝再激活的影响，并根据最大剥落深度、宽度和总裂缝表面积的增加进行定量评估。总体而言，本文提供的模拟表明，热剥落会增加剥落区的深度（远离钻孔）和角宽度，但不太可能导致裂缝孔径的大幅增加，并随之增加剥落区的水力传导率和渗透性，高于已经由机械剥落引起的水平。